In the prior art, the amplitude of the analog signal being converted has been automatic gain controlled to a given reference level for its maximum and minimum amplitudes. However, it is difficult to change the gain of a signal without detrimentally affecting its bandwidth.
The present approach of logically detecting and combining the digital bits of the converted signal in such a manner that a determination can be made as to whether the A/D converter reference voltage should be raised or lowered to improve the conversion accuracy, eliminates any problems with altering bandwidth. Additionally, the automatic gain control circuitry and bandwidth compensation circuitry is eliminated and the savings in circuitry accordingly reduces expense of the total apparatus.
It is therefore an object of the present invention to provide an improved method of compensating for varying analog multilevel representative signals by adjusting the reference voltages to an analog-to-digital converter.